This invention relates to providing a rigid-flex circuit board system which can be produced more efficiently and has greater functionality than prior art rigid-flex circuit boards. In the past, manufacturing rigid flex circuit boards has been problematic. Many factors, difficult to control given current manufacturing techniques, result in high scrap rates (circuit boards that do not work). For example, in the past, it has been troublesome to align flexible printed circuit layers with rigid printed circuit layers since the flexible printed circuit layers are not dimensionally stable (the flexible portions stretch, warp, shrink, etc.). This dimensional instability introduces a significant degree of variability in the manufacturing process. On a rigid printed circuit board, the location of the traces, and the pads for drilling and mounting components, etc. can be located with great reliability. Rigid board manufacturing processes can typically rely on determining the locations of the traces and pads etc. from registering just a couple points on the rigid board. With flexible printed circuit boards, locations of traces and pads cannot be as reliably mapped and registered since the flexibility results in the traces and pads etc., shifting by variable amounts. As a result, when flexible printed circuit layers are laminated to rigid circuit boards the connections between the two layers (at the interface) may not be aligned properly throughout due to the inconsistencies caused by dimensional instability of the flexible layer (with the result that the circuit board will not work properly, and must be scrapped, which is wasteful and expensive). In order to increase reliability (and reduce scrap) in manufacturing rigid-flex circuit boards, more expensive machinery and more complicated processes are used (than for manufacturing standard rigid boards). In the past, those attempting to reduce scrap, utilizing available manufacturing techniques, have also sacrificed the number and density of connections between the rigid and flexible layers, since these connections have been problematic (for the above reasons). However, as is well known in the industry, achieving higher densities can have many benefits (such as, for example, reduced size, reduced energy consumption, increased speed, etc.).
Further, even if the flexible layers are successfully connected to the rigid layers, later manufacturing steps are often still troublesome (and more expensive than standard rigid board manufacturing) as a result of the dimensional instability (variable stretching) introduced by the flexible portions. For example, reliability in soldering components to a rigid-flex board may be reduced due dimensional instability. Any fabrication and component assembly process involving handling the rigid-flex boards may be complicated due to portions of the board “flopping around” etc.
In the past (since mechanical support is needed during the assembly process of placing components, reflow of the solder process, and for installation in the housing, etc.) stiffeners (without conductive layers and without electrical connections/function) have been added to flex layers to provide such mechanical support. Also, in the past, manufacturing flexible circuits has been complicated by the need to use stabilization frames and/or rigid leaders and/or specialty plating racks in order to provide support for flexible portions of circuit boards during the manufacturing process. These methods add complexity, cost and increased scrap rates, to the manufacturing process.
These are just a few of the many complications that make manufacturing and manipulating flexible and rigid-flex circuit boards more difficult and expensive than standard rigid boards.